Transmission of power from a wind turbine generator to a utility grid is generally AC power transmission. However, an increase in the length of a power transmission line to the utility grid will increase the inductive reactance, thus limiting the power that can be transmitted.
Thus, a series capacitor is sometimes connected to the power transmission line to decrease (offset or compensate for) the inductive reactance. Connection of the series capacitor to the power transmission line increases the transmissible power. However, since the inductive reactance of the wind turbine generator and the power transmission line forms a serial resonant circuit, a resonance phenomenon occurs depending on the grid configuration and the state of the load, which can damage electrical equipment connected to the grid.
Thus, the following methods have been proposed as countermeasures to be taken when resonance occurs.
A bypass filter (blocking filter) is connected in parallel to the series capacitor connected in series to the power transmission line. A compensating unit that operates actively, such as a thyristor-controlled series capacitor (TCSC), is installed at a current collecting point, such as a substation.
The above two methods need a filter having a capacity corresponding to the power transmission capacity or the amount of power generated by the plant and a compensating unit, thus causing the problem of increasing the cost.
On the other hand, PTL 1 discloses a method for actively suppressing the amplitude of a resonance component under excitation control whereby a resonance component is detected from a current, and a current in a rotor winding of a generator provided in a wind turbine generator is controlled using a power converter. Since the method disclosed in PTL 1 uses existing facilities of the wind turbine generator, an increase in cost for suppressing the resonance component can be reduced.